ACTION research is an attempt to seek immediate solutions to the problems experienced in educational settings. In this type of research, teachers are the researchers who intend to make instant reforms to develop, and improve their teaching styles and reflect on pedagogical practices. The purpose of this study was to conduct an ACTION research to tackle the problem of students’ low motivation in English CLASSes at the medical school of Iran University of Medical Sciences in fall 2010. Participants of this study were 98 thirdsemester ESP students of medicine. To reform the situation and promote students’ motivation to participate in CLASSes more actively and eagerly, the researchers changed the syllabus by applying Kemmis and McTaggart’s (1988) cyclical model of ACTION research, and adopting task-based teaching. Data was collected by means of interviews with both teachers and students to determine the changes to be made in the syllabus, CLASSroom observations to monitor students’ behavioral changes, and a questionnaire to assess students’ attitudes towards the changes. This research study had a number of valuable outcomes the most important of which was a change in CLASSroom behavior of the students.